1.Field of the Invention
The present invention relates to an electroluminescence (EL) display apparatus and its driving method, and more particularly, to an EL panel display apparatus and its driving method that are capable of easily setting a color balance and improving a luminance.
2.Description of the Background Art
Recently, various panel display devices are being developed to reduce a weight and a volume of a cathode ray tube. The panel display devices include a field emission display (FED), a plasma display panel (PDP) and an electro-luminescence (EL) display.
The EL display utilizes an EL phenomenon that a light is generated by a voltage applied to a phosphor layer. Thanks to its rapid response speed, low DC drive voltage and capability of being ultra-thin compared to such an LCD, the EL display can be adoptable to a wall-hanging type product or a portable product.
The EL displays are classified into an inorganic EL display and an organic EL display depending on its material and structure.
FIG. 1 is a drawing illustrating the cell structure of the inorganic EL panel in accordance with a conventional art.
As shown in FIG. 1, the cell 10 of the inorganic EL panel includes: an upper insulation layer 4 and a lower insulation layer 2, a phosphor layer 3 formed between the lower and upper insulation layers 2 and 4, a back electrode 1 formed on the lower insulation layer 2, and a clear electrode 5 formed on the upper insulation layer 4. The clear electrode 5 is formed at a rear surface of a glass substrate 6.
The upper and lower insulation layers 2 and 4 are made of a dielectric material. Thus, when a voltage is applied to the cell 10, the upper and lower insulation layers 2 and 4 have a certain capacitance.
The phosphor layer 3 is excited by electrons to emit a visible light. The phosphor layer 3 is made of an inorganic substance such as Zns or Mn.
The back electrode 1 is made of a conductive material such as Al. The back electrode 1 receives a scan pulse from a gate driving unit (not shown). That is, the back electrode 1 is used as a scan electrode for supplying the scan pulse to the cells 10.
The clear electrode 5 is made of a clear conductive material such as Indium-Tin-Oxide (ITO). The clear electrode 5 receives a data pulse from a data driving unit (not shown). That is, the clear electrode 5 is used as a data electrode for supplying the data pulse to the cells.
When the scan pulse is supplied to the back electrode 1 and the data pulse is applied to the clear electrode 5 (that is, a voltage is applied between the back electrode 1 and the clear electrode 5), holes are accelerated toward the back electrode 1 and electrons are accelerated toward the clear electrode 5. The electrons and the hole collide at the central portion of the phosphor layer 3. When the electrons and the hole collide, the phosphor layer 3 generates a visible light to display a certain image.
FIG. 2 is a drawing illustrating the inorganic EL display in accordance with the conventional art.
As shown in FIG. 2, the conventional inorganic EL display includes: a panel 13 consisting of data lines D1˜Dn, scan lines S1˜Sm and cells 10 positioned at cross points between the data lines D1˜Dn and the scan lines S1˜Sm; a data driving unit 12 for supplying a data pulse to the data lines D1˜Dn; and a scan driving unit 11 for supplying a scan pulse to the scan lines S1˜Sm.
The operation of the conventional inorganic EL display will now be described.
First, the scan driving unit 11 sequentially supplies a scan pulse to the scan lines S1˜Sm.
The data driving unit 12 supplies a data pulse in synchronization with the scan pulse to the data lines D1˜Dn.
At this time, upon receiving the scan pulse and the data pulse, the pixel cell 10 emits a visible light corresponding to the data pulse to display a picture.
The phosphor layer 3 included in the pixel cell 10 and generating light of red (R), green (G) and blue (B) is made of different materials. That is, red and green fluorescent materials are made of Zns:Mn, and the ratios of Zns and Mn respectively contained in the red and green fluorescent material differ. The blue fluorescent material is made of Cas:Mn.
Zns signifies a compound of zinc and sulfur, Mn signifies manganese, and Cas signifies a compound of calcium and sulfur, which will now be described with reference to FIGS. 3A and 3B.
FIGS. 3A and 3B are graphs showing voltage-luminance characteristics of red, green and blue inorganic materials.
As shown in FIGS. 3A and 3B, comprised of different components, threshold voltages of red, green and blue fluorescent materials are different from each other.
That is, as shown in FIG. 3A, though different depending on the ratio and the amount of the material contained therein, the blue fluorescent material is emitted at a threshold voltage of 120˜200V.
As shown in FIG. B, the red and green fluorescent material differ according to a ratio or an amount of a contained material but emits at a threshold voltage between approximately 150˜240V.
Thus, in order to make the red, green and blue fluorescent materials to luminesce at the different threshold voltages, a scan pulse with a lower voltage than the lowermost threshold voltage of the different threshold voltages is supplied to the red (R), green (G) and blue (B) fluorescent materials.
At this time, different voltages of the data pulse are supplied to the red, green and blue fluorescent materials to display a picture, for which the data driving unit 12 includes an R driving unit 12A for emitting red light from the red fluorescent material, a G driving unit 12B for emitting green light from the green fluorescent material and a B driving unit 12C for emitting blue light from the blue fluorescent material.
However, disadvantageously, the blue fluorescent material in the EL panel of the conventional art has a considerably short life span compared with that of the red and green fluorescent material.
In addition, the blue fluorescent material of the EL panel of the conventional art has a considerably low luminance compared with that of the red and green fluorescent material. That is, since the luminance of the blue fluorescent material is low compared to that of the red and green fluorescent material, it is difficult to set a color balance.
Moreover, since it is difficult to set the color balance of the fluorescent material of the EL panel, a luminance is degraded.